1. Field of the Invention
The invention relates in general to the field of data networking and communications, and in particular to interconnecting computers to a local area network (xe2x80x9cLANxe2x80x9d) or a wide area network (xe2x80x9cWANxe2x80x9d) through data lines that carry power, network data and telephone data.
2. Description of the Related Art
Network devices, such as networked personal computers, typically communicate via wired data lines and receive power from a separate line. For example, personal computers (xe2x80x9cPCsxe2x80x9d) may communicate ethernet signals via category three (CAT-3) or category five (CAT-5) twisted pair wire and receive power from a second cable connected to a power source, such source, such as a wall socket or a battery. However, it is desirable to be able to eliminate the need for the second cable.
The following describes examples of network devices that benefit from the elimination of the separate power line, and then describes some of the inadequacies of previous solutions.
Plain old telephone service (xe2x80x9cPOTSxe2x80x9d) combines a voice signal with a power signal. The combined signal is transmitted over twisted pair cable between the telephone and the line card at the public telephone exchange office. The line card also supplies power over the two wires carrying the voice signal. However, the voice signal supported by POTS is not sufficient for bandwidth intensive communications needs, such as, ethernet communications. Similarly, ISDN communications transmit power and digital data over between an ISDN modem and a telephone switch. However, ISDN data rates are more than an order of magnitude lower than ethernet data rates.
Additionally, telephone systems using private bridge exchanges (PBXs) typically have a wired connection that is separate from the network devices. This additional wired connection carries both telephone data signals and power to the telephone. The telephone data signals may be either digital or analog data signals that carry the voice conversations to and from the PBX to a telephone. The PBX is responsible for relaying the voice conversation to and from other users or out into the public telephone exchange. The PBX also supplies the telephone with power. In the event of a power outage, the PBX may have a back up power supply to allow users to continue to use their phones during the power outage.
POTS does have one important feature which is supported by some PBX systems. During a power failure, the telephone continues to operate. This is because power is supplied to the telephone directly from a backup power system at the PBX or the central switch. This is a desirable feature of telephone systems.
In previous systems where a user has both a network device and a telephone, the user will have a cable connected to the network for network communications with the network device, a cable connected to a power source for the powering the network device, and a cable connected to the PBX for powering and carrying communications to and from the telephone. One problem with such a system is the cost of installing and maintaining all of these cables. Therefore, it is desirable to have a system that supplies the same general network device and telephone functionality to the user, but reduces the significant cabling costs of the system.
Therefore, what is needed is a solution that reduces the wiring requirements to transmit data and power to a network device and a telephone without significantly reducing the functionality of the network device and the telephone.
One embodiment of the invention includes an apparatus for providing electric power to a telephone across a transmission line where the telephone is coupled to a network device. A power and data coupler (xe2x80x9cthe couplerxe2x80x9d) is coupled to one end of the transmission line. The transmission line is also adapted for transmission of a data signal. The data signal includes telephone signal data for communications with the telephone. The coupler has a data input and a power input. Power from the power input is coupled to the data signal from the data input and the combined power supply current and data signal is coupled to one end of the transmission line. The opposite end of the transmission line is coupled to a power and data decoupler (xe2x80x9cthe decouplerxe2x80x9d). The decoupler has a power output and a data output. Both the data output and power output of the decoupler are coupled to the network device. The combined power and data signal is decoupled by the decoupler, and the data signal is supplied to the data output and the power is supplied to the power output. The invention also includes a telephone circuit. The telephone circuit receives the power from the power output and receives the telephone signal data. The telephone circuit couples the power and the telephone signal data together to make a combined power and telephone signal, which can be used by the telephone.
In another embodiment, the invention includes a power switch to selectively switch between power from the decoupler and power from an external source. In one embodiment, the power switch selects power from the decoupler when a power outage, for example, causes the external power source to cease supplying power.
In another embodiment, the transmission line includes two transmission lines. One of the transmission lines carries both data and power signals. In another embodiment, data and power signals are carried on both of the transmission lines.
In other embodiments, the power signal includes alternating current and/or direct current.
In another embodiment, the transmission lines include twisted pair cables. These features of the invention will be apparent from the following description which should be read in light of the accompanying drawings.